The present invention is directed to a method for purifying water and, more particularly, to a method for producing ultrapure, pyrogen-free water that can be used as a pharmaceutical solvent for injection into humans or other animals.
Since water is an excellent solvent, it finds many uses in the pharmaceutical and electronics industries, such as for rinsing, sterilizing and intravenous solutions. However, such uses for water require that the water be ultrapure, pyrogen-free. As used herein, "ultrapure, pyrogen-free" water is water that has a specific electrical resistance of at least 18 million ohms/cm (18 meg ohms/cm), and contains no pyrogens. Traditionally, water of such purity has been produced by distillation, which removes pyrogens, preceded by mixed-bed deionization. Indeed, the U.S. Food and Drug Administration ("FDA") requires that water for injection be water purified by either distillation or reverse osmosis. As used herein, "water for injection" is defined as water that satisfies the FDA's purity requirements for water for injection. Distillation, however, is a very energy consuming and costly method for producing water for injection.
U.S. Pat. No. 4,280,912 to Berry et al discloses producing water for injection by passing the water through the following treatment units: a bed of absorbent carbonaceous resin; an ion-exchange resin deionization bed; an ultra-violet energy source; and a resin polishing bed. However, Berry et al's feed water must have a minimum electrical resistance of 500,000 ohms/cm, which necessarily implies that Berry et al requires previously treated feed water. Single glass distillation, for example, produces water that has a specific electrical resistance of 500,000 ohms/cm.
It has been known for many years that ozone can be used in processes for treating water. For example, in U.S. Pat. No. 799,605 to Lester, an apparatus is disclosed to purify water that sequentially passes the water through an electrolytic chamber, an ozonizing chamber, a charcoal filter, a coarse sand filter, and a fine sand filter. However, Lester's system does not remcve minerals and pyrogens and cannot produce ultrapure water.
U.S. Pat. No. 4,069,153 to Gunther discloses a method for purifying water that uses both ultraviolet radiation and ozone. More specifically, Gunther irradiates water with ultraviolet radiation of 1849 angstroms to convert oxygen dissolved in the water into ozone. According to Gunther, ozone enhances pyrogen destruction and provides a synergistic, or at least additive effect, with the ultraviolet radiation per se on the molecular alteration of pyrogens. However, Gunther's feed water is pretreated by distillation, and his method is not capable of producing ultrapure water.
Finally, U.S. Pat. No. 4,230,571 to Dadd discloses a method wherein ultraviolet radiation of 1850 angstroms generates ozone from air, the ozone generated is mixed with the water to be purified, and the water/ozone mixture is then subjected to ultraviolet radiation of 2600 angstroms. According to Dadd, the ultraviolet radiation has a catalytic effect on the reaction of ozone with bacteria, viruses and undesirable compounds in the water. Dadd's method does not produce pyrogen-free or ultrapure water.